Combustion control



Aug. 1, 1944. "r. LADD 2,354,999

COMBUSTION CONTROL:

Filed Feb. 26, 1941 I III I INVENTOR- 7240 14 1400.

' 7 g g. an.

Patented Aug. 1, 1944 COMBUSTION CONTROL Tallman Ladd, Garden .City, N. Y., assignor to Combustion Engineering Company, Inc.,' New York, N. Y.

Application February 26, 1941, Serial No. 380,591

3 Claims.

I The present invention relates to apparatus for controlling the combustion of fuel in a furnace and particularly to means for minimizing the dangers incidental to disruption of the supply or burning of fuel in furnaces where an explosive mixture of fuel and air is fed to the furnace.

In furnaces where the fuel is a mixture of pulverized coal, gas or oil with air, there is danger that an accidental discontinuance of the fuel supply and consequent flame extinction may result in filling the furnace with a highly explosive mixture in the event that the re-establishment of and air is burned, although it is to be understood that it is likewise applicable to furnaces in which the fuel is gas or oil. The raw coal from the bin I0 is delivered by a feeder II toa pulverizing mill l2. An exhauster fan I3 withdraws the pulverized coal from the mill l2 and the stream of coal and air is fed through a conduit Hi to the supplyof fuel occurs and the fuel is not immediately ignited.

It also happens that when pulverized coal is burned in a furnace, temporaryvariations in the rate of fuel supply may occur with the result that a spasmodic flame is produced in. the furnace. Under such conditions it is also possible that the flame may go out while the supply of fuel to the furnace may be resumed when the condition causing the discontinuance or interruption of the fuel supply is corrected, either because of attention by the operators or as a result of thefuel feeding apparatus returning to normal operating conditions.

When retardation'or complete interruption of the supply of fuel to the furnace occurs, the volume of gases within the furnace decreases. This results in an increase in draft in the furnace. In accordance with the invention the rise in draft in the furnace consequent upon disruption of the fuel supply is utilized to control the apparatus by means of which fuel is supplied to and burned in the furnace.

A feature of the invention resides in placing auxiliary fuel feeding burners in operation when the main supply of fuel is disrupted in order to reignite the latterwhen the supply is resumed.

Another feature resides in controlling the apparatus providing the main supply of fuel vwhen a disruption occurs so as to gradually reduce the rate of fuel supply by increments rather than immediately discontinue it entirely, thereby avoiding unnecessary complete stoppages of the main fuel supply. A further feature of this control phase is that the operation of the controls to reduce the rate of fuel supply offsets the increase that would otherwise result with automatic combustion controls from a decrease in boiler output consequent upon failure of combustion as indicated by draft increase.

The invention will be best understood upon reference to the following detailed description when read in conjunction with the accompanying drawing in which the single figure is a diagrammatic view of a fuel burning system embodying the present invention. I

The invention will be described as embodied in a furnace in which a mixture of pulverized coal one or more burners l'5 which introduce it into the furnace IS. The feeder II is driven by an electric motor I! and both the pulverizer l2 and exhauster fan l3 by a single motor IR. A draft is induced in the furnace l6 by means'of a fan 20 mounted in the ofitake of boiler 2| as to withdraw the products of combustion from the furnace. A bellows 22 arranged so as to respond to fluctuations in boiler pressure is connected by the rod 23 to the arms 24, 25 of rheostats associated with the motors I1 and It for driving the feeder II and the min [2 and fan l3, respectively. A

decrease in boiler pressure causes the bellows 22 to act to move the rheostat arms so as to speed up the motors to increase the rate of fuel supply. An increase in boiler pressure has an opposite effect upon these motors.

Mounted closely adjacent to the burner I5 are several auxiliary burners 30 so located with respect to the main burners that the flames of these auxiliary burners spread across the path of or partly overlap the fuel stream suppled by the main burners. The auxiliary burnersare supplied with a fuel which may be instantly ignited upon entering the furnace, such as oil supplied through the feed line 3| by a fuel pump 32 driven by a motor 33.

The motors I1, I8 and 33 for driving feeder I I, pulverizing mill l2 and exhauster fan l3 and the fuel supply pump 32 are connected to a source of 1 electrical power designated 34. The switches or rheostats which control the motor circuits (not illustrated in detail) are connected to the cores of solenoids 4|, 42 and 40, respectively. These solenoids are in turn under the control of a switch 43 which, when opened, de-energizes all of them. As represented in the drawing, the switch 43 is connected to a diaphragm 44 subject to the pressure existing .in the furnace l6 transmitted through a conduit 45. The opening of switch 43 is opposed by a spring 46 which is of such force and so arranged that the switch remains closed until the pressure in the furnace IE decreases to a predetermined value.

When the furnace I6 is in normal operation, pulverized coal and air are fed through the conduit [4 to the main burners IS in amounts sufficient to carry the load. The induced draft fan 20 is adjusted to produce a draft capable of adequately removing the products of combustion from the'furnace.- If reduction or complete interruption of the supply of fuel to the furnace occurs, the volume of gases in the furnace degization of the solenoid ll! the associated spring 50 closes a switch i connecting the motor 33 of the fuel oil supply pump 32 as well as an ignition coil for. the auxiliary burner 30 to the power line 34. Consequently, a supply of auxiliary fuel to the furnace is promptly established and is ignited therein. Hence, although the flame of the main burner l5 may have gone out and although a mixture of coal and air may be continued to be supplied thereto, this mixture would be immediately ignited by the flames of the auxiliary burners, thus avoiding a possible explosion.

The solenoids II and 42 also were de-energized at the tim the auxiliary burners were placed in operation. Upon solenoid 4i being de-energized, a spring 52 acts to open a switch 53 to cut off power to the motor I! which drives the fuel feeder ll. When the solenoid 42 is de-ener- 'gized, a, spring 54 acts on rheostat arm 55 to diminish the power supplied the motor l8, thus slowing down the pulverizing mill and exhauster fan. Consequently the rate of fuel supplied to the main burners is reduced as the fan l3 slows down. The slowing down of the motorfor fan i3 is preferably effected in stepped increments which may be accomplished by providing the rheostat arm 55 with a roller. engageable with steps 51 on a pivoted cam-like lever 58 which is connected to a dashpot 60 so that the latter retards the downward movement of the rheostat arm 55 under the force of spring 54. The stepby-step slowing down of the mill'and fan from normal operation to a full stop permits-operation ergized, cutting of! the fuel supply and ignition coil of the auxiliary burners II and placing the feeder motor IT in operation again as well as the motor 18 that drives the mill l2 and fan II. Preferably the closing of the switch 43 is retarded as by a dashpot 41 so as to maintain the auxiliary burners in operation for an interval of time during which temporary instability or extinguishment of the flames of the main burners may be corrected. For example, the flames of the main burners may, because of spasmodic choking within the mill l2, vary between its normal 'and a diminished intensity. The furnace draft would correspondingly vary between its normal and a higher value and this would cause the switch 43 to be opened whenever the draft exceeded. the selected predetermined value and to be immediately closed again as the draft fell to anormal value. Dashpot 4T prevents this underesponsive to decrease to a predetermined value at reduced speeds for an interval which in many cases may be sumcient to enable a clogged or similar condition in the coal supply line to be corrected by continued operation and without attention from the operator. Thus unnecessary complete discontinuance of coal supply is avoided while at the same time dangerous. conditions in furnace l6 are avoided because the auxiliary burners 30 cause combustion of any coal and air mixture entering the furnace.

When the main bumers i 5 go out or the flames therefrom diminish in intensity because of clogging in some part of the fuel supply system causing a diminution of the rate of fuel supply, the output of the boiler drops. Consequently,

. with the combustion control apparatus illustrated bellows 22 acting on rheostats 24, 25 for motors l1, l8 would ordinarily act to increase the rate of fuel supply by increasing the rate of feeder H and the mill l2 and fan l3. However, the deenergization of solenoid 42 results in the downward movement of the other rheostat arm 55 for motor l8 which offsets the action of the combustion control tending to supply more coal by acting in a sense to decrease the speed of motor is while permitting it to remain temporarily in operation. a

' When normal conditions are restored, the increase in the pressure in the furnace ii to its normal value results in permitting the spring 45 to act to reclose the switch 43. Consequently the solenoids 40, 4| and 42 would again be en.

of the pressure existing in said furnace for operating said control means for said main burners to stop said fuel supply means and to place said auxiliary burners in operation; and means acting on said control means for said supply means to retard the stopping thereof.

2. In a furnace having main fuel burners". means for supplying a mixture of fuel and air to said burners, means for creating a draft in said furnace, and control means governing the opera tion of said fuel supply means; auxiliary burners mounted to introduce fuel into the furnace at points so closely adjacent to the point at which the main burners introduce fuel that burning fuel from the auxiliary burners ignites fuel introduced into the furnace by the main burners; means for supplying fuel to said auxiliaryburners; control means for placing said auxiliary burners in operation; and means responsive to decrease to predetermined value of the pressure existing in said furnace for operating said control means to stop said main fuel supply means and to place said auxiliary burners in operation.

3. In a furnace having fuel burners, means for supplying a mixture of fuel and air to said burners, means for creating a draft in said furnace, and control means governing the operation of said fuel supply means; auxiliary burners mounted to introduce fuel into the furnace at points so closely adjacent to the point at which the main burners introduce fuel that burnin fuel from the auxiliary burners ignites fuelintroduced into the furnace by the main burners; means for supplying fuel to said auxiliary burners; controlv means for placing said auxiliary burners in operation; means responsive to decrease to a predetermined value of the pressure existing in said furnace for operating said control means to stop said main fuel supply means and to place said auxiliary burners in operation; and means acting on said control means for said supply means for the main burners to retard the Stopping thereof.

TAILMAN LADD. 

